The Asiana Airlines pilots whose Boeing 777 crashed Saturday while landing at San Francisco International Airport were following a routine visual approach and didn't radio any onboard problems or declare an emergency before impact, according to preliminary reports.

Investigators will now focus on why the twin-engine jetliner—arriving on an overnight flight from Seoul and descending in good weather—slammed down hard on a portion of the airport hundreds of feet before the runway's normal touchdown point, according to...